With the rapid development of optical communications technologies, a PON system is increasingly widely applied in optical communications technologies. A PON architecture is shown in FIG. 1, and the architecture is used as an example for description below. A PON consists of an optical line terminal (OLT) 110 on an office side, an optical network unit (ONU) 120 (or an optical network terminal (ONT)) on a user side, and an optical distribution network (ODN) 130. A tree topology structure is generally used in the PON.
The OLT 110 provides a network side interface to the PON system to connect one or more ODNs 130. The ONU 120 provides a user side interface to the PON system to connect the ODN 130. If the ONU 120 directly provides a function of a user port, for example, an Ethernet user port used by a personal computer (PC) to access the Internet, the ONU 120 is referred to as the ONT 120. Unless otherwise indicated, the ONU 120 mentioned below generally refers to the ONU and the ONT. The ODN 130 is a network consisting of an optical fiber and a passive optical splitter configured to connect the OLT 110 and the ONU 120 and further configured to perform distribution or multiplexing on a data signal between the OLT 110 and the ONU 120.
In the PON system, a direction from the OLT 110 to the ONU 120 is referred to as a downstream direction. In contrast, a direction from the ONU 120 to the OLT 110 is referred to as an upstream direction. In a gigabit-capable PON (GPON), based on a specification in the current International telecommunication Union (ITU) G.984 series standards, a downstream transmission rate is generally 2.488 gigabits per second (Gbps) (i.e. 2488 megabits per second (Mbps)), and only one downstream transmission rate exists during running of the entire system.
Generally, in design of an optical network, to ensure that required performance levels are reached in various optical transmission sections, a budget of a total optical power loss needs to be planned, where the budget is referred to as an optical power budget. Losses allowable in the optical power budget are defined as optical losses S/R and R/S (S denotes a reference point of optical signal sending, and R denotes a reference point of optical signal receiving) between reference points, which are expressed in decibels (dB). The loss includes a loss caused by an optical fiber and a loss caused by a passive optical element. In an existing ODN network, an optical power budget may become insufficient because an optical link loss increases. Therefore, how to increase an optical power budget of a PON system is a problem that urgently needs to be resolved.